Optical detector, optical head device, optical information processing device, and optical information processing method

ABSTRACT

A photodetector, includes: a semiconductor chip that converts received light to an electric signal; and a resin body that encapsulates the semiconductor chip. The photodetector further includes a protective unit, and at least a light transmission area, through which the light passes, in a surface of the resin body on an incident side of the light is covered by the protective unit. Covering the light transmission area with the protective unit that is less in reactivity with light than the resin body can suppress deformation of the resin body due to light, thus suppressing deterioration of the optical characteristics of the photodetector.

TECHNICAL FIELD

The present invention relates to a photodetector and an optical headdevice, an optical information processing device and an opticalinformation processing method using the photodetector.

BACKGROUND ART

Optical memory technology utilizing high-density and large-capacityoptical storage media having a pit-formed pattern has been applied to adigital audio disc, a video disc, a document file disc and further adata file, etc. During the 1980s, compact discs (CD) that record andreproduce information by irradiation with light having a wavelength ofabout 780 nm became commercially practical, and during the 1990s,digital versatile discs (DVD) became commercially practical, which canrecord and reproduce higher density and larger amounts of informationthan the CDs by irradiation with light having a wavelength of about 650nm. Both of these are used commonly today.

In the above optical memory technology, information is recorded andreproduced with respect to an optical storage medium by a minutelycollected light beam. The accuracy and reliability of these recordingand reproduction operations depend critically on the accuracy andreliability of an optical head device. Essential functions of theoptical head device are roughly classified into: a function ofconverging light output from a light source to a minute spot diameter onthe order of the diffraction limit; and a function of detecting a signalrequired for focus control so as to maintain a light spot on the opticalstorage medium, a signal required for tracking control so as to positionthe light spot at a midpoint of a specific track and a pit signal.

Meanwhile, one element constituting the optical head device is aphotodetector. The photodetector receives light reflected from theoptical storage medium, converts it into an electric signal(photoelectric conversion), detects an information signal recorded onthe optical storage medium (hereinafter referred to as “RF signal”), afocus error signal (hereinafter referred to as “FE signal”), a trackingerror signal (hereinafter referred to as “TE signal”) and the like,which are signals required for recording and reproducing, and outputsthese signals. The photodetector also is used for receiving a part ofthe light emitted from the light source so as to control an output fromthe light source.

The above-described photodetector generally conducts the photoelectricconversion using a semiconductor with a photoelectric conversion areaand, if required, a circuit attached thereto built therein. In order tocarry out reliable recording and reproducing, needless to say, thephotodetector also is required to have high reliability.

FIG. 7 shows one example of a conventional photodetector. Asemiconductor chip 51 is secured onto a lead frame 54, and an electrodeon the semiconductor chip 51 and a lead of the lead frame 54 areconnected electrically via a bonding wire 55. The lead frame 54 is aterminal for inputting/outputting electric signals and electric power,and the photodetector is connected electrically with a flexible printedwiring board (not illustrated) and the like via the lead frame 54. Thesemiconductor chip 51, the bonding wire 55 and a part of the lead frame54 are encapsulated within a resin body 52 having a light-transmittingproperty. The resin body 52 protects the bonding wire 55, a junctionbetween the semiconductor chip 51 and the bonding wire 55, a surface ofthe semiconductor chip 51 with a circuit and the like built therein, andso on in order for these portions not to break due to a shock during thehandling.

Light 56 reflected from the optical storage medium and containing asignal component having information recorded on the optical storagemedium and the like passes through the resin body 52 and reaches aphotoelectric conversion area 51 a on the semiconductor chip 51 toundergo the photoelectric conversion. The photoelectrically convertedsignal travels through the bonding wire 55 to be output from the leadframe 54 as an electric signal. To this end, a material having anecessary transparency with respect to the light 56 and a favorablemoldability, e.g., an epoxy resin is used as the resin body 52 (See JPS63(1988)-830 A, pp 1 to 2, FIG. 6, for example).

In recent years, an optical storage medium that allows recording andreproducing of still higher-density and larger-capacity information thanthat in DVDs has been developed, with the intention of shortening awavelength of a light source used for the recording and reproducing ofinformation with respect to such an optical storage medium from a redlight source (wavelength of about 660 nm) to a blue light source(wavelength of about 400 nm). However, when a wavelength of light usedfor the recording and reproducing with respect to an optical storagemedium is changed to, for example, about 400 nm, a light transmissionarea 61 of the light-transmissive resin 52 in the photodetector shown inFIG. 7 will be deformed gradually over a few hours to a few hundredhours due to the light incident on the photodetector. This adverselyaffects an optical path of the light passing through the lighttransmission area 61, thus making it impossible for the light reflectedfrom the optical storage medium to reach the photoelectric conversionarea 51 a on the semiconductor chip 51 while maintaining a correctprofile. As a result, the photodetector cannot detect desired electricsignals such as a FE signal and a TE signal sufficiently. Therefore, anoptical information processing device using an optical head deviceincluding such a photodetector has a problem of the failure in adequateoperations by a focus control unit and a track control unit.

In addition, there is another problem of a decrease in the amplitude ofa RF signal, which impairs the reliability of reproducing.

Also in a photodetector that has a function of detecting a signal usedfor judging the magnitude of a light amount to control an output from alight source and outputting the signal, if the resin body 52 is deformedsignificantly, a part of the light does not reach the photoelectricconversion area 51 a due to reflection, diffraction and the like. Thisleads to a problem of the failure in the precise detection of theabove-stated signals.

DISCLOSURE OF THE INVENTION

A photodetector of the present invention includes: a semiconductor chipthat converts received light to an electric signal; and a resin bodythat encapsulates the semiconductor chip. The photodetector furtherincludes a protective unit, and at least a light transmission area,through which the light passes, in a surface of the resin body on anincident side of the light is covered by the protective unit.

An optical head device of the present invention includes: a lightsource; a condensing unit that receives light emitted from the lightsource and collects the light onto an optical storage medium; and aphotodetector that receives light reflected from the optical storagemedium and converts the light to an electric signal. The photodetectorincludes: a semiconductor chip that converts received light to anelectric signal; and a resin body that encapsulates the semiconductorchip. The photodetector further includes a protective unit, and at leasta light transmission area, through which the light passes, in a surfaceof the resin body on an incident side of the light is covered by theprotective unit.

An optical information processing device of the present inventionincludes: an optical head device that includes a light source, acondensing unit that receives light emitted from the light source andcollects the light onto an optical storage medium, and a photodetectorthat receives light reflected from the optical storage medium andconverts the light to an electric signal; an electric signal processingunit that receives a signal output from the optical head device andoutputs a predetermined signal; and a driving unit that receives thepredetermined signal so as to change a position of at least one selectedfrom the optical head device and the condensing unit. The photodetectorincludes: a semiconductor chip that converts received light to anelectric signal; and a resin body that encapsulates the semiconductorchip. The photodetector further includes a protective unit, and at leasta light transmission area, through which the light passes, in a surfaceof the resin body on an incident side of the light is covered by theprotective unit.

An optical information processing method of the present invention isembodied using an optical information processing device that includes:an optical head device that includes a light source, a condensing unitthat receives light emitted from the light source and collects the lightonto an optical storage medium, and a photodetector that receives lightreflected from the optical storage medium and converts the light to anelectric signal; an electric signal processing unit that receives asignal output from the optical head device and outputs a predeterminedsignal; and a driving unit that receives the predetermined signal so asto change a position of at least one selected from the optical headdevice and the condensing unit. The photodetector includes: asemiconductor chip that converts received light to an electric signal;and a resin body that encapsulates the semiconductor chip, and thephotodetector further includes a protective unit, and at least a lighttransmission area, through which the light passes, in a surface of theresin body on an incident side of the light is covered by the protectiveunit. In the case where a transmittance of light having a wavelength ofλ1 with respect to the resin body is 10%, a wavelength λ of the lightsource satisfies a relationship of λ1<λ<1.5·λ1.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a relationship between a wavelength of light incident on aphotodetector and a transmittance of the light.

FIG. 2 is a cross-sectional view showing one embodiment of aphotodetector of the present invention.

FIG. 3 is a cross-sectional view showing another embodiment of aphotodetector of the present invention.

FIG. 4 is a cross-sectional view showing still another embodiment of aphotodetector of the present invention.

FIG. 5 shows a configuration of one embodiment of an optical head deviceof the present invention.

FIG. 6 schematically shows one embodiment of an optical informationprocessing device of the present invention.

FIG. 7 is a cross-sectional view showing one example of a conventionalphotodetector.

BEST MODE FOR CARRYING OUT THE INVENTION

The following describes embodiments of the present invention further indetail. Firstly, details for arriving at the present embodiments will beexplained below.

FIG. 1 shows a relationship between a wavelength of light incident onthe photodetector shown in FIG. 7 and a transmittance of the light. Inthe photodetector shown in FIG. 7, the resin body 52 is made of an epoxyresin and has a thickness d of 1 mm.

As shown in FIG. 1, the transmittance of the light is almost constant ina region of the wavelength of the light longer than 450 nm and decreasesgradually with a decrease in wavelength in a region shorter than 450 nmso as to be about 0 at the wavelength of about 320 nm. Although most ofthe light absorbed by the resin body 52 is turned to heat so as to beradiated, part of the absorbed light becomes an energy source forcutting covalent bonds of the resin making up the resin body 52.

When energy required for cutting the covalent bonds is converted usingthe relational formula of E=h·c/λ (E: energy, h: Planck constant, λ:wavelength, c: speed of light) so as to be represented by a wavelengthpossessed by a photon, a wavelength of light required for cutting asingle bond ranges from 300 to 400 nm, and a wavelength of lightrequired for cutting a double bond ranges from 150 to 200 nm. Therefore,when the resin body 52 is irradiated with light having a wavelengthlonger than 400 nm, the energy for disconnecting the double bond cannotbe achieved at all and the energy for disconnecting the single bond ishardly achieved, and therefore it has been considered that the resinbody 52 will not be deformed.

However, in the case where a temperature for using the photodetectorreaches 270 K to 350 K, there is a probability, albeit a lowprobability, that a covalent bond is cut by the light with a wavelengthlonger than 400 nm also.

In addition, since a diameter of the light collected to be incident onthe photoelectric conversion area 51 a is as small as about 10 μm, whichmeans that a light density per unit area is significantly high in thephotoelectric conversion area 51 a, the resin body 52 might generatemultiphoton absorption in which two or more photons are absorbedconcurrently. For example, when the resin body 52 generates two-photonabsorption, then the resin 52 with transparency absorbs energy twicethat of the reaction with one photon, and a covalent bond might be cutby such energy.

The resin making up the resin body 52 contains atoms such as carbon,hydrogen and oxygen, where these atoms are bonded with one anothercovalently. When these covalent bonds are cut by irradiation of theresin body 52 with light, these atoms become active. Normally, if theirradiation with light is ceased, the activated atoms return to theoriginal bonding state. However, it has been found that when the lighttransmission area 61 is irradiated with light in an atmosphere of oxygenbeing present, a covalent bond of an oxygen molecule that exists in thevicinity of the light transmission area 61 also is cut. Since the oxygenatoms also become active, the atom whose covalent bonding has been cutbonds with the oxygen atom, thus deforming the resin body 52 gradually.

Thus, the inventors of the present invention arrived at an idea ofcovering at least a light transmission area through which light passesin a surface of a resin body 2 on a light incident side with alight-transmissive protective unit in order for this area not to contactwith oxygen.

Embodiment 1

FIG. 2 is a cross-sectional view showing one embodiment of aphotodetector of the present invention. The photodetector of thisembodiment, as shown in FIG. 2, includes a semiconductor chip 1, a leadframe 4, a bonding wire 5, a resin body 2 having a light-transmittingproperty and a protective layer 3 having a light-transmitting property.The semiconductor chip 1 is mounted on the lead frame 4, and thesemiconductor chip 1 and the lead frame 4 are connected electrically viaa bonding wire 5. The semiconductor chip 1, the bonding wire 5 and apart of the lead frame 4 are encapsulated with the resin body 2. On asurface of the resin body 2 on an incident side of a converged light 6,the protective layer 3 is laminated so that at least a lighttransmission area 11 through which the converged light 6 passes does notcontact with oxygen in the air.

According to the photodetector of this embodiment, since the surface ofthe resin body 2 on the incident side of the converged light 6 iscovered with the protective layer 3 at least at the light transmissionarea 11 through which the converged light 6 passes, the followingadvantages can be obtained, for example: even when the resin body 2 isirradiated with high-density light in order to detect a FE signalaccurately or to detect a noise ratio to a RF signal accurately, whichwould activate atoms contained in the resin body 2 in the lighttransmission area 11, the bonding of the thus activated atoms with anoxygen atom can be suppressed, thus allowing the deformation of theresin body 2 and the deterioration of optical characteristics of thephotodetector to be suppressed. According to the photodetector of thisembodiment that thusly enables the suppression of the deterioration ofthe optical characteristics, signals such as a FE signal, a TE signaland a RF signal can be detected and output accurately.

The semiconductor chip 1 includes a photoelectric conversion area 1 aand a circuit 1 b that are built therein, where the photoelectricconversion area 1 a converts received light to a current signal and thecircuit 1 b amplifies the current signal output from the photoelectricconversion area 1 a and converts the same to a voltage signal.

The lead frame 4 contains a conductive material, for example, metalssuch as Cu and an alloy (Fe—Ni), and in a state where the lead frame 4is secured to a wiring board such as a flexible printed wiring board bya method of soldering and the like, the lead frame 4 functions as aterminal for inputting and outputting an electric signal such as thecurrent signal or the voltage signal and electric power.

The bonding wire 5 is a thin metal wiring, e.g., a thin gold wiring,which delivers the current signal or the voltage signal obtained fromthe semiconductor chip 1 to the lead frame or supplies the semiconductorchip 1 with electric power.

A material of the protective layer 3 is not limited especially as longas the material does not react so much with light and oxygen and has alight transmittance of a predetermined value or higher. However, aninorganic substance having bond dissociation energy larger than that ofan organic substance such as an epoxy resin is preferable. Inparticular, the material preferably includes at least one type ofinorganic compound selected from the group consisting of silicon oxide,silicon nitride, magnesium fluoride and tantalum oxide. This is becausethese inorganic compounds can double as an insulation film of thesemiconductor chip and an antireflection film of an optical component,which can reduce the number of the types of materials to be used and thenumber of manufacturing apparatuses, thus reducing a cost.

The protective layer preferably has a transmittance of light, which issubstantially incident thereon except for a light amount reflected fromthe surface, of 90% or more and more preferably 95% or more. This isbecause a higher transmittance of light leads to a lower absorptance ofthe light, which suppresses a deterioration due to the light. It can beconsidered that when the transmittance is 90% or more, there is littledeterioration of the protective layer due to light and when thetransmittance is 95% or more, there occurs no deteriorationsubstantially.

Unlike the resin body 2, there is no need to give the protective layer 3a function for encapsulation, and therefore there is no need to form theprotective layer 3 by a transfer molding method in which a molten resinis poured. Although a method for forming the protective layer 3 is notlimited especially, it preferably is formed by, for example, sputtering,evaporation or spin coating, which facilitates the formation of theprotective layer 3.

Although a thickness of the protective layer 3 is determinedappropriately depending on the working conditions of the photodetector,a preferable thickness is 20 nm or more when the photodetector is usedin a general optical head device where a wavelength of a light source iswithin a range of 390 nm to 420 nm and a power of the converged light 6ranges from a few hundreds μW to a few mW. This is because, when thethickness is too small, there is a possibility of oxygen in the air andwater vapor passing therethrough. Since water vapor contains oxygenatoms, when the water vapor passes through the protective layer 3, thereis a possibility of the resin body 2 being deformed similar to the casewhere the resin body 2 is irradiated with light and an atmosphere ofoxygen is present. In the case of the photodetector with the protectivelayer 3 of 20 nm or more in thickness, the deformation of the resin body2 is not found even after the use over a few thousand hours, and signalssuch as a FE signal, a TE signal and a RF signal can be detected andoutput accurately.

Furthermore, it is preferable that the protective layer 3 is provided soas to function as an antireflection film. This is because, when theprotective layer 3 has an antireflection function, a loss of light dueto reflection can be reduced, and therefore an optical gain efficiencyof the photodetector can be enhanced. The material and the thickness ofthe protective layer 3 may be determined based on a method for designingthe antireflection film. Note here that a method for designing theantireflection film is generally well-known, so that explanations forthat will be omitted.

A material of the resin body 2 is not limited especially as long as thematerial has a desired transmittance with respect to the light incidentthereon. In addition, since the photodetector of this embodiment isequipped with the protective layer 3, the material of the resin body 2can be selected while giving a priority to a favorable moldabilityrather than a resistance to deterioration due to the reaction withlight. For instance, an epoxy resin, polycarbonate, polyolefin and thelike can be used, and in particular it preferably contains an epoxyresin, which applies little load to the bonding wire 5 during themolding, is easily molded and has a favorable moldability under a lowpressure.

Preferably, an absorptance of the light by the resin body 2 is 10% orless (transmittance of 90% or more). This is because, when theabsorptance of the light by the resin body 2 is 10% or less, aphotodetector can be provided with a still reduced tendency for thedeformation of the light transmission area 11 due to the received light.

After the semiconductor chip 1 is mounted on the lead frame 4 and thesemiconductor chip 1 and the lead frame 4 are connected electrically viathe bonding wire 5, the resin body 2 is formed by a transfer moldingmethod and the like so that a surface of the resin body 2 on a lightincident side becomes parallel with a surface of the semiconductor chip1. A thickness d between the light incident side surface of the resinbody 2 and the surface of the semiconductor chip 1 with thephotoelectric conversion area 1 a formed thereon is set at 1 mm, forexample.

According to the explanations with reference to FIG. 2, the lightincident on the photodetector is light that is reflected from theoptical storage medium and is converged. However, the light may be apart of the light emitted from the light source and the photodetectormay be provided for detecting a signal used for controlling an outputfrom the light source.

Furthermore, although the circuit 1 b is provided on the semiconductorchip 1 in the illustrated example of FIG. 2, this is not limited to thatexample. As shown in FIG. 2, when the circuit 1 b is provided on thesemiconductor chip 1, heat is generated in the semiconductor chip 1 by acurrent flowing through the circuit 1 b. As a temperature of the resinbody 2, i.e., a temperature of the semiconductor chip, becomes higher,the degree of the deformation of the resin body 2 becomes moreremarkable. When the circuit 1 b is formed at a position away from thephotoelectric conversion area 1 a in the semiconductor chip or isprovided at another portion of the photodetector that is notencapsulated with the resin body 2, the transmission of the heatgenerated in the circuit 1 b to the light transmission area 11 can besuppressed, thus suppressing the deformation of the resin body 2, andenabling more stable detection and output of signals such as a FEsignal, a TE signal and a RF signal.

Note here that although the semiconductor chip 1 and the lead frame 4are connected electrically using the bonding wire 5 in the illustratedexample of FIG. 1, a method for connecting the semiconductor chip 1 andthe lead frame 4 is not limited especially. They may be connected bywireless bonding such as a flip-chip method. In the case where wirelessbonding is adopted for the connection method, an injection moldingmethod and other types of methods, which are conducted at highertemperatures and under higher pressures than in the transfer moldingmethod, can be applied, thus enhancing the flexibility in amanufacturing method.

Furthermore, although the protective layer 2 is a single layer in theillustrated example of FIG. 2, this is not limited to that example. Theprotective layer 3 may have a multilayered structure in which two ormore layers made of different materials are laminated.

Embodiment 2

FIG. 3 is a cross-sectional view showing one embodiment of thephotodetector of the present invention. In FIG. 3, the same referencenumerals are assigned to the elements having the same functions as thoseof the elements shown in FIG. 2 and their explanations will be omitted.

In the photodetector of this embodiment, instead of the protective layer3 (See FIG. 2), a light transmission area 11 is covered with a flatplate member 7, a sealing member 8 and inert gas in order for the areanot to contact with oxygen in the air. The plate member 7 has alight-transmitting property and is disposed at least above the lighttransmission area 11. The sealing member 8 bonds the plate member 7 witha resin body 2 and is located so as to be away from the lighttransmission area 11, and the inert gas is enclosed in a space 9surrounded by a surface of the resin body 2 on an incident side of light6, the plate member 7 and the sealing member 8.

In the photodetector of this embodiment, at least the light transmissionarea 11 in the surface of the resin body 2 on the incident side of thelight 6 is covered with a protective unit including the plate member 7,the sealing member 8 and the inert gas enclosed in the space 9.Therefore, similarly to Embodiment 1, for example, even when the resinbody 2 is irradiated with the high-density converged light 6, whichwould activate atoms contained in the resin body 2 at the lighttransmission area 11, the bonding of the thus activated atoms with anoxygen atom can be suppressed, thus enabling the suppression of thedeformation of the resin body 2. As a result, according to thephotodetector of this embodiment, signals such as a FE signal, a TEsignal and a RF signal can be detected and output accurately.

A material of the plate member 7 is not limited especially as long asthe reaction with oxygen is sufficiently less than the resin body 2 orthere occurs no reaction with oxygen when being irradiated with lighthaving a predetermined wavelength, and it has a desired transmittancewith respect to the light incident thereon. For example, silica glassand borosilicate glass are preferable.

The plate member 7 preferably has a transmittance of light, which issubstantially incident thereon except for a light amount reflected fromthe surface, of 90% or more and more preferably 95% or more. This isbecause a higher transmittance of light leads to a lower absorptance ofthe light, which suppresses a deterioration due to the light. It can beconsidered that when the transmittance is 90% or more, there is a littledeterioration of the plate member 7 due to light and when thetransmittance is 95% or more, substantially no deterioration occurs.

Although the type of the inert gas enclosed in the space 9 is notlimited especially as long as it does not react with the resin body 2when being irradiated with light and does not hinder the transmission ofthe light, and it preferably includes nitrogen, which is available at alow cost. For example, in the case where a wavelength of the lightincident on the photodetector is within a range of 390 nm<λ<420 nm, theinert gas enclosed in the space 9 may be argon. Furthermore, gas otherthan inert gas may be enclosed in the space 9, and oxygen may beincluded if it is included at about 1/10 (about 2.5%) or less of theoxygen concentration in the air.

These gases can be enclosed in the space 9 easily by assembling thephotodetector of this embodiment in an atmosphere of these gases.

The sealing member 8 preferably is one having a small amount ofoutgassing therefrom (1% or less), such as an ultraviolet-curingadhesive, a silicone-based adhesive and an epoxy-based adhesive. This isbecause the outgas generated from the sealing member 8 and mixed intothe inert gas in the space 9 is combined with atoms on the surface ofthe resin body 2 when the outgas is activated by irradiation with light.Although the degree of the combination depends on the intensity of theirradiated light, if the combined outgas forms a lens on the surface ofthe resin body 2, a deviation of a condensing position on the resin body2 occurs. This results in the failure of the light to be received by thesemiconductor chip 1 successfully.

As shown in FIG. 3, in the embodiment where the sealing member 8 islocated away from the light transmission area 11, there are nolimitations on the light-transmitting property of the sealing member 8at all. However, in the case where the sealing member 8 has a desiredtransmittance with respect to the incident light, i.e., is substantiallytransparent with respect to the incident light, the space 9 may befilled with the sealing member 8. That is to say, the protective unitthat covers the light transmission area 11 to prevent the lighttransmission area 11 from contacting with oxygen may be configured witha plate member 7 and a sealing member 10, as shown in FIG. 4, where theplate member 7 is disposed above a surface of the resin body 2 on anincident side of light, and the sealing member 10 bonds at least thelight transmission area 11 of the surface of the resin body 2 on thelight incident side with the plate member 7 and has a light-transmittingproperty.

Note here that although the incident light side surface of thelight-transmissive plate member 7 of the photodetector is planar in theembodiments shown in FIG. 3 and FIG. 4, it may be a lens-form or ahologram-form so that the light 6 can have a desired wavefront such asastigmatism or may have an optical function such as splitting a part ofthe light 6, whereby a small optical head device can be realized.

Embodiment 3

FIG. 5 shows one embodiment of the optical head device of the presentinvention. As shown in FIG. 5, the optical head device includes asemiconductor laser 21, as a light source, capable of emitting laserlight with a wavelength in the range of 390 nm <λ<420 nm, a condensinglens 23, a mirror 24 for bending an optical path, an objective lens 25,a beam splitter 27 for separating returning light reflected from anoptical storage medium 26 and a photodetector 28. As the photodetector28, the photodetector of Embodiment 1 or Embodiment 2 is used.

When information recorded on the optical storage medium 26 isreproduced, laser light 22 emitted from the semiconductor laser 21having a wavelength of 405 nm, for example, becomes parallel light bythe condensing lens 23, and an optical path thereof is bent by themirror 24. Then, the light is collected onto the optical storage medium26 by the objective lens 25. Next, the light reflected from the opticalstorage medium 26 returns to the objective lens 25, the mirror 24 andthe condensing lens 23 in this order, and is reflected from the beamsplitter 27 so as to enter the photodetector 28. The light incident onthe photodetector 28 undergoes photoelectric conversion by thephotodetector 28 and the photodetector 28 detects a RF signal of a pitrow on the optical storage medium 26, a FE signal for carrying outtracing of the pit row and a TE signal and outputs these signals.

Although operations during recording basically are the same as thoseduring the reproduction, the amount of light emitted from thesemiconductor laser is larger in the recording than in the reproduction.

Since the optical head device of this embodiment employs thephotodetector of Embodiment 1 or Embodiment 2, the optical head devicecan receive accurate FE signals, TE signals and RF signals from thephotodetector 28, so that favorable recording/reproducing can berealized.

In the case where a transmittance of light having a wavelength of λ1with respect to the resin body 2 of the photodetector 28 (See FIGS. 2 to4) is 10%, it is preferable that the wavelength λ of the semiconductorlaser (light source) satisfies a relationship of λ1<λ<1.5·λ1. When thewavelength of the light source satisfies the above relationship, adeterioration of the resin body 2 due to light can be suppressed, thusenabling the provision of a reliable optical head device that canrealize favorable recording/reproducing.

Particularly, the wavelength λ of the light source preferably is in therange of 390 nm <λ<420 nm. This is because not only the cutting of adouble bond but also the cutting of a single bond can be suppressedeffectively, while a high-reliability optical head device capable ofrecording/reproducing with respect to high-density and large-capacityoptical storage media can be provided.

Note here that although the optical head device of this embodimentemploys the photodetector so as to detect RF signals, FE signals and TEsignals, the photodetector may be used for detecting a monitor signalfor controlling an output from the light source. In this case, anoptical head device can be provided so as to realize stable control ofthe output and favorable recording/reproducing.

Embodiment 4

FIG. 6 schematically shows one embodiment of the optical informationprocessing device of the present invention. As shown in FIG. 6, theoptical information processing device includes: an optical head device31; an electric signal processing unit 33 that receives a signal outputfrom the optical head device 31 and calculates the signal to output apredetermined signal; a driving unit (not illustrated) that receives thepredetermined signal so as to change a position of at least one selectedfrom the optical head device 31 and a condensing unit 25 (objectivelens) (See FIG. 5) of the optical head device 31; a motor 32 and a powersupply device 34.

The electric signal processing unit 33 is a circuit board, for example.The power supply device 34 is a power source or a connection terminalfor an external power supply, which supplies electricity to the motor 32and the driving unit. The power source or the connection terminal for anexternal power supply may be provided for each driving unit such as atracking control unit and a focus control unit.

Since the optical information processing device of this embodimentemploys the optical head device of Embodiment 3, the optical informationprocessing device can receive accurate FE signals, TE signals and RFsignals from the photodetector of the optical head, so that favorablerecording/reproducing can be realized.

In an optical information processing method embodied using the opticalinformation processing device of this embodiment, when a wavelength of alight source 21 (See FIG. 5) of the optical head is assumed as λ andwhen a transmittance of light having a wavelength of λ1 with respect tothe resin body 2 of the photodetector (See FIGS. 2 to 4) is 10%, it ispreferable that the wavelength λ of light from the light source 21satisfies a relationship of λ1<λ<1.5·λ1. When the wavelength of lightemitted from the light source satisfies the above relationship, adeterioration of the resin body 2 due to light can be suppressed, thusallowing favorable recording/reproducing to be realized.

Particularly, the light source preferably emits light having thewavelength λ of 390 nm <λ<420 nm. This is because not only the cuttingof a double bond but also the cutting of a single bond can be suppressedeffectively, while recording/reproducing with respect to high-densityand large-capacity optical storage media is enabled.

INDUSTRIAL APPLICABILITY

According to the photodetector, the optical head device, the opticalinformation processing device and the optical information processingmethod of the present invention, the deterioration of opticalcharacteristics of the photodetector can be suppressed, thus enablingfavorable recording/reproducing.

1. A photodetector, comprising: a semiconductor chip that convertsreceived light to an electric signal; and a resin body that encapsulatesthe semiconductor chip, wherein the photodetector further comprises aprotective unit, and at least a light transmission area, through whichthe light passes, in a surface of the resin body on an incident side ofthe light is covered by the protective unit.
 2. The photodetectoraccording to claim 1, wherein the protective unit is a protective layerthat is laminated on the surface of the resin body on the incident sideof the light.
 3. The photodetector according to claim 2, wherein theprotective layer comprises an inorganic substance.
 4. The photodetectoraccording to claim 3, wherein the inorganic substance comprises at leastone type of inorganic compound selected from the group consisting ofsilicon oxide, silicon nitride, magnesium fluoride and tantalum oxide.5. The photodetector according to claim 2, wherein the protective layerhas a function of antireflection.
 6. The photodetector according toclaim 2, wherein the protective layer is formed by sputtering,evaporation or spin coating.
 7. The photodetector according to claim 1,wherein the protective unit comprises: a plate member that is disposedabove the surface of the resin body on the incident side of the light; asealing member that bonds the plate member and the resin body and islocated away from the light transmission area; and an inert gas enclosedin a space surrounded by the surface of the resin body on the incidentside of the light, the plate member and the sealing member.
 8. Thephotodetector according to claim 7, wherein the inert gas comprisesnitrogen.
 9. The photodetector according to claim 1, wherein theprotective unit comprises: a plate member that is disposed above thesurface of the resin body on the incident side of the light; and asealing member that bonds at least the light transmission area in thesurface of the resin body on the incident side of the light with theplate member.
 10. The photodetector according to claim 1, wherein theresin body comprises an epoxy resin.
 11. The photodetector according toclaim 1, wherein an absorptance of the light by the resin body is 10% orless.
 12. An optical head device, comprising: a light source; acondensing unit that receives light emitted from the light source andcollects the light onto an optical storage medium; and a photodetectorthat receives light reflected from the optical storage medium andconverts the light to an electric signal, wherein the photodetector,comprises: a semiconductor chip that converts received light to anelectric signal; and a resin body that encapsulates the semiconductorchip, wherein the photodetector further comprises a protective unit, andat least a light transmission area, through which the light passes, in asurface of the resin body on an incident side of the light is covered bythe protective unit.
 13. The optical head device according to claim 12,wherein in the case where a transmittance of light having a wavelengthof λ1 with respect to the resin body is 10%, a wavelength λ of the lightsource satisfies a relationship of λ1<λ<1.5·λ1.
 14. The optical headdevice according to claim 12, wherein the wavelength λ of the lightsource is in a range of 390 nm <λ<420 nm.
 15. An optical informationprocessing device, comprising: an optical head device that comprises: alight source; a condensing unit that receives light emitted from thelight source and collects the light onto an optical storage medium; anda photodetector that receives light reflected from the optical storagemedium and converts the light to an electric signal, wherein thephotodetector, comprises: a semiconductor chip that converts receivedlight to an electric signal; and a resin body that encapsulates thesemiconductor chip, wherein the photodetector further comprises aprotective unit, and at least a light transmission area, through whichthe light passes, in a surface of the resin body on an incident side ofthe light is covered by the protective unit; an electric signalprocessing unit that receives a signal output from the optical headdevice and outputs a predetermined signal; and a driving unit thatreceives the predetermined signal so as to change a position of at leastone selected from the optical head device and the condensing unit. 16.An optical information processing method embodied using an opticalinformation processing device that comprises: an optical head devicethat comprises: a light source; a condensing unit that receives lightemitted from the light source and collects the light onto an opticalstorage medium; and a photodetector that receives light reflected fromthe optical storage medium and converts the light to an electric signal,wherein the photodetector, comprises: a semiconductor chip that convertsreceived light to an electric signal; and a resin body that encapsulatesthe semiconductor chip, wherein the photodetector further comprises aprotective unit, and at least a light transmission area, through whichthe light passes, in a surface of the resin body on an incident side ofthe light is covered by the protective unit; an electric signalprocessing unit that receives a signal output from the optical headdevice and outputs a predetermined signal; and a driving unit thatreceives the predetermined signal so as to change a position of at leastone selected from the optical head device and the condensing unit,wherein in the case where a transmittance of light having a wavelengthof λ1 with respect to the resin body is 10%, a wavelength λ of the lightsource satisfies a relationship of λ1<λ<1.5·λ1.
 17. The informationprocessing method according to claim 16, wherein the light source emitslight having a wavelength λ of 390 nm <λ<420 nm.